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Ring‐fused aminal is an interesting structural skeleton in biologically active and pharmaceutically relevant compounds. A novel and efficient method for synthesizing benzosulfamidate‐fused tetrahydroquinazolines is described. By employing the [4+2]‐cycloaddition of 2‐aminophenyl enones with cyclic N‐sulfimines in the presence of DMAP as a base, the desired benzosulfamidate‐fused tetrahydroquinazolines were obtained in good yields with high diastereoselectivities. Furthermore, an organocatalytic asymmetric [4+2]‐cycloaddition was successfully achieved using a squaramide‐based catalyst, enabling the enantioselective synthesis of chiral ring‐fused tetrahydroquinazolines with high yields and enantio‐ as well as diastereoselectivities (up to 89 % yield, 94 % ee, and >30 : 1 dr). [ABSTRACT FROM AUTHOR]